cannot find symbol public void configureFlutterEngine(#NonNull FlutterEngine flutterEngine) - flutter

Question

I am getting this error while trying to register plugin in MainActivity.java file
Error log
: error: cannot find symbol
public void configureFlutterEngine(#NonNull FlutterEngine flutterEngine) {
^
MainActivity.java
package com.orsac.bluis;
import io.flutter.embedding.android.FlutterActivity;
public class MainActivity extends FlutterActivity { #Override public void configureFlutterEngine(#NonNull FlutterEngine flutterEngine) {
GeneratedPluginRegistrant.registerWith(flutterEngine); }
}
In AndroidManifest.xml file, getting Unresolved class error in android:name=".UniappApplication" and android:name=".MainActivity"
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.orsac.bluis">
<application
android:name=".UniappApplication" // Here
android:label="BLUIS"
android:usesCleartextTraffic="true"
android:networkSecurityConfig="#xml/network_security_config"
android:icon="#mipmap/ic_launcher">
<activity
android:name=".MainActivity" // Here
android:launchMode="singleTop"
android:theme="#style/LaunchTheme"
android:configChanges="orientation|keyboardHidden|keyboard|screenSize|smallestScreenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
android:hardwareAccelerated="true"
android:windowSoftInputMode="adjustResize">
<intent-filter>
<action android:name="android.intent.action.MAIN"/>
<category android:name="android.intent.category.LAUNCHER"/>
</intent-filter>
<intent-filter>
<action android:name="FLUTTER_NOTIFICATION_CLICK" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<!-- Don't delete the meta-data below.
This is used by the Flutter tool to generate GeneratedPluginRegistrant.java -->
<meta-data
android:name="flutterEmbedding"
android:value="2" />
</application>
Things I Tried
Flutter clean
Flutter run
Invalidate caches and restart

Answer 1

You should import androidx.annotation.NonNull;
import androidx.annotation.NonNull;

Answer 2

1- Update targetSdkVersion and compileSdkVersion to the latest and equal version in build.gradle(app level) under android section
2- Import these libraries in MainActivity
import io.flutter.embedding.android.FlutterActivity;
import io.flutter.embedding.engine.FlutterEngine;
import io.flutter.plugins.googlemobileads.GoogleMobileAdsPlugin;